The present technology relates to the operation of memory devices.
Semiconductor memory devices have become more popular for use in various electronic devices. For example, non-volatile semiconductor memory is used in cellular telephones, digital cameras, personal digital assistants, mobile computing devices, non-mobile computing devices and other devices.
A charge-storing material such as a conductive floating gate or a non-conductive charge-trapping material can be used in such memory devices to store a charge which represents a data state. The memory cell may be a transistor in which the charge-storing material may reside between a channel and a control gate. The charge-storing material may be insulated from both the channel and the control gate. The charge-storing material can be arranged vertically in a three-dimensional (3D) stacked memory structure, or horizontally in a two-dimensional (2D) memory structure. One example of a 3D memory structure is the Bit Cost Scalable (BiCS) architecture which comprises a stack of alternating conductive and dielectric layers.
In one arrangement, memory cells are arranged in strings having a select gate transistor at each end to selectively connect a channel of the string to a source line at one end and bit line at the other end. The string may have a number of data memory cells and one or more dummy memory cells. If present, a dummy memory cell is typically located between a select gate transistor and the data memory cells. There may be one or more dummy memory cells at each end of the string. The control gates of the memory cells are connected to word lines in some architectures. The word lines that connect to control gates of data memory cells are typically referred to as data word lines. The word lines that connect to control gates of dummy memory cells are typically referred to as dummy word lines. Note that in some architectures the control gates of certain memory cells may share a common “word line.” For example, memory cells on neighboring strings may share the same word line.
Memory cells may be programmed by altering the charge in the charge-storing material, thereby altering the threshold voltage of the memory cell transistor. The charge in the charge-storing material may be controlled using Fowler-Nordheim tunneling or hot-electron injection, for example. In one technique, a high voltage is applied to the control gate with a low voltage in the channel to add charge to the charge-storing material.
When programming a memory cell (referred to herein as a “selected memory cell”), memory cells that are not currently selected for programming (referred to herein as “unselected memory cells”) may receive some unintentional programming. This unintentional programming is referred to herein as “program disturb.” This program disturb may occur to unselected memory cells that share the same word line as the selected memory cell. In order to reduce or eliminate the program disturb, the voltage in the channels of the unselected memory cells may be boosted. Therefore, the voltage differential between the control gate and channel of the unselected memory cell may be low enough to reduce or eliminate unintentional programming of the unselected memory cells. However, challenges remain in preventing or reducing program disturb.